Field of the Invention
The invention is in the field of medical technology and concerns a method and an implant for stabilizing a plurality of separated bone portions relative to each other in a human or animal patient, wherein the bone portions to be stabilized are in particular two bone portions being separated by osteotomy or fracture but may also be two originally articulating bones to be immobilized relative to each other (joint fusion, in particular fusion of small joints such as e.g. facet joints, finger or toe joints).
Description of Related Art
Osteotomy is a surgical procedure in which a bone is cut with the aim of being shortened, lengthened or re-aligned. Osteotomy is performed on human and animal patients mainly for realigning the load bearing surfaces in joints and for realigning bone portions in particular in the facio-maxillar region but also for re-aligning bone portions healed together with an undesired alignment relative to each other after a fracture. The bone portions separated by the osteotomy procedure mostly need to be aligned in a desired position relative to each other and to be stabilized in this position for being able to heal together again. According to the state of the art, osteotomy sites are usually stabilized with the aid of a plate (e.g. metal plate) which is positioned on the bone surface across the osteotomy cut and is fastened on each side thereof with the aid of bone screws which extend through the plate into the bone tissue. According to the state of the art simple bone fractures are stabilized and small joints are immobilized in the same manner.
Well known applications of osteotomy concern e.g. human hip or knee joints and serve for re-aligning the articular surfaces of the joint in order to correct dysplasias and deformities by improvement of the alignment and/or the interaction of the articulating bones, or for relieving arthritic pain by re-aligning partly damaged articular surfaces to shift the bearing of the load from damaged to still healthy regions of the articular surfaces. Further well known osteotomy applications concern mandible or maxilla re-alignment e.g. for correcting discrepancies in tooth positions, or concern the chin bone for correcting or improving a person's profile. In veterinary medicine osteotomy is used e.g. for treating canine stifle joints suffering from cranial cruciate ligament rupture or damage by tibial plateau leveling or tibial tuberosity advancement, both these treatments serving for reducing tibiofemoral shear forces during weight bearing, which shear forces become large enough for damaging the joint, when the cranial cruciate ligament is damaged.
Screw and plate systems are well established for stabilizing bone portions separated by a cut or fracture and for immobilizing joints, although they constitute severe constraints which in many cases prevent optimal solutions. The most important ones of these constraints are the necessarily circular cross section of the screws, the reduction of the ratio of the load bearing capability of the screws vs. their cross section due to the screw thread, and the fact that the plate is necessarily positioned on the bone surface and, for accommodation of the screw heads and for being able to keep plate and screw rigidly at a predetermined angle relative to each other, has in most cases a thickness which is larger than would be necessary for guaranteeing a satisfactory plate stiffness.